Refining inflation using non-canonical scalars

TL;DR

This paper demonstrates that non-canonical scalar field models can enhance inflationary theory by improving compatibility with CMB data, notably reducing tensor-to-scalar ratios and allowing steep potentials to drive inflation.

Contribution

It provides closed-form solutions and shows how non-canonical scalars can make previously incompatible inflation models viable, including steep potentials and the exponential type.

Findings

Non-canonical scalars decrease tensor-to-scalar ratio.

Steep potentials can drive inflation in non-canonical models.

Non-canonical models violate the standard consistency relation.

Abstract

This paper revisits the Inflationary scenario within the framework of scalar field models possessing a non-canonical kinetic term. We obtain closed form solutions for all essential quantities associated with chaotic inflation including slow roll parameters, scalar and tensor power spectra, spectral indices, the tensor-to-scalar ratio, etc. We also examine the Hamilton-Jacobi equation and demonstrate the existence of an inflationary attractor. Our results highlight the fact that non-canonical scalars can significantly improve the viability of inflationary models. They accomplish this by decreasing the tensor-to-scalar ratio while simultaneously increasing the value of the scalar spectral index, thereby redeeming models which are incompatible with the cosmic microwave background (CMB) in their canonical version. For instance, the non-canonical version of the chaotic inflationary potential, $V(\phi) \sim \lambda\phi^4$, is found to agree with observations for values of $\lambda$ as large as unity ! The exponential potential can also provide a reasonable fit to CMB observations. A central result of this paper is that {\em steep potentials} (such as $V \propto \phi^{-n}$) usually associated with dark energy, can drive inflation in the non-canonical setting. Interestingly, non-canonical scalars violate the consistency relation $r = -8n_T$, which emerges as a {\em smoking gun} test for this class of models.